The Commonwealth of Massachusetts is a leader in forcing the removal of lead from dwellings. The older houses and apartments were often painted with lead paints which have a faintly sweet taste attractive to some children. Since lead is a neurotoxin which has been shown to retard brain development and functions, lead is routinely removed from residences by the requirements of various Massachusetts State Laws. This Massachusetts concern has subsequently been reflected in the Laws and Regulations of many other jurisdictions. On a Federal level, the EPA has reflected the concern with lead by strict potable water testing procedures for lead indicating concerns about lead content of water at the highest levels of government.
The deleading process for buildings typically involves scraping or chemical removal of paint on specified surfaces to a statutorily determined height and often also requires wood replacement. Mere scraping alone as a method to remove the paint is insufficient since lead compounds and salts soak into pores and grain on the surface of wood. The Chemical removal process using alkaline gels containing solvents and strippers such as trisodium phosphates reaches the soaked in salts but the chemical strippers must be flushed from the surface and the surface must be neutralized as part of the removal process. Especially in the chemical removal process, a water wash is needed to remove traces of lead remaining on the wood as well as to neutralize the chemical strippers. In dry scraping a wash is still needed to reduce and remove dust and particles and to do a final cleaning of the wood. The removed paint is a lead containing hazardous waste and must be disposed of properly by use of licensed waste handling firms. The paint solids are relatively dense and total solids generation is typically only a drum per house. The wash water is many times the volume of the solids removed. The wash water also contains significant lead contents and must also be removed as a hazardous waste. Since the cost of hazardous waste removal in MA is slightly over $400 per 55 gallon barrel, and since at least 5 barrels of this contaminated water are produced for a typical deleading job, there is a considerable cost for waste water removal in each deleading operation.
In the past much waste water found its way into drains and sewers. This potential contamination of potable water supply and destruction to marshes and rivers was ignored. A result of this and other contaminants being added to rivers is the toxic nature of local harbor mud. Now, there is tighter enforcement of removal and tracing of wastes so this illegal use of local sewers is being halted. Tracing of all disposal streams and insuring waste streams are treated properly should continue to be an area of increasing concern. Despite the concern and the rules, no one has found an ecconomic way to stop the easy profits to be made by illegal dumping of these washwater waste streams. There is thus a need for a detailed tracing system for wastes or for a simple method to eliminate the wastes on site and thus eliminate the temptations to illegally dump wastes, especially those wastes that are dilute and not obvious There is a need for site treating of the waste water to reduce its impact on deleading costs and to make environmental compliance more likely.
The problem of deleading is not restricted to household deleading operations. There are numerous bridges, oil tanks and other steel structures that were painted with lead pigment containing protective coatings. These are often red lead primers as well as other paint materials. This lead paint is a problem for workers on or near the tanks as the paints deteriorate and also leaches into the water supply when the surfaces are contacted by acid rain or other pollution. In many construction projects on bridges, the workers, who are now aware of lead hazards, will not start on steel work until the structure has been deleaded.
The bridge deleading experience in Massachusetts has been especially difficult. Some early sandblasted deleading projects created so much contaminated dust that the surrounding area became seriously contaminated and numerous houses had to have lead containing dust removed. The current requirement for bridge deleading is to use vacuum protected sandblasting, needle guns, or chemical deleading compounds. The two allowed mechanical deleading processes are very slow while there is contaminated wastewater generated by the chemical processes requirement for neutralization and washdown. A process to treat or reduce wastewater from chemical deleading would allow this process to dominate the field since it is quick and easy as compared to the other allowable processes. Chemical methods are also dust free.
There are a series of methods that have been attempted to solve the contaminated wastewater problem. The most common legal way to solve the low level contaminated water problem is to truck it to a processing facility where it is concentrated with elaborate chemical treatments. It can be then landfilled in class 1 or class 3 hazardous waste landfills. Another common method is to first evaporate the water, then when there is a concentrated fraction left, disposing of the smaller concentrated stream by trucking to a chemical plant which is cheaper since there is less volume. The costs are totally related to volume and not to content so concentration is a viable way to save on disposal. In other cases ion exchange resins and ion specific chemicals have been used. The chemicals to remove lead in moderate concentrations in water are either expensive to use or are very slow to react.
Some approaches use just a settling step such as the Johnson U.S. Pat. No. 4,898,678 but the settling taught by Johnson is for particulate lead metal, not the dissolved salts that are a problem in deleading cleanups.
An example of expensive chemical beneficiation of lead contaminated wastewater is the use of EDTA reagents to remove heavy metals. These metal combinant chemicals, used widely to chelate lead and in labs, are very expensive. Chemical approaches are noted in Patents such as Rothman U.S. Pat. Nos. 4,222,897 & 4,338,288 where a sorbant of Manganese nodules with occluded sulfur is used for deleading of waste streams. In another chemical approach Sayles in U.S. Pat. No. 4,954,230 used Methane di-sulfonic acid as a deleading approach. A precipitation method suggested by Zeijlstra in U.S. Pat. No. 4,338,200 uses a hydroxide precipitation in closely controlled temperature and pH ranges to remove lead.
An example of the slow processes is carbonate reduction of the waste water where solid wastes are mixed with lime and an agent containing carbon dioxide and/or bicarbonate to reduce the solids to a non leachable form. Such a concept may allow a carbonate reduction of liquids also. This is shown in U.S. Pat. No. 4,137,339. The process indicated is interesting and is effective if the solutions and reactions are kept cold but this system is less effective as temperature increases and the process is slow. Since chemical deleading processes are most effective at room or higher temperatures, the need for cool reactions is not an advantage. There is still a need for a simple and effective reaction process to remove lead at low cost.
Another process is the use of electrolysis to obtain electrolytic metallic precipitin on a stainless steel cathode followed by absorber columns in U.S. Pat. No. 4,954,230 by Rudolph Kirch where the metal is precipitated on a stainless screen. This type process is effective only for high levels of lead and is energy inefficient at low concentration levels.
At present the expensive and fast chemical removal processes or the very slow but high removal quality methods can be used.
No basic removal system is available which meets the requirements of quick yet relatively low cost lead removal of dissolved lead that is at moderate to high lead content levels.
There are other solutions designed for very low lead content fluids. Lead removal from water is done in several environments presently. Drinking water lead removal has become a major industry. While the rationale of this need is dubious, the use of ion exchange resins and reverse osmosis is effective only to lower trace amounts of lead. The size of the reverse osmosis units and the cost of the units make these approaches useful only for trace amounts.
Included in the potable water deleading systems are a variety of complex methods for removal of trace amounts of lead, they usually include several steps. One common system combines a ion exchange column with a carbon bed absorber. In another a low volume reverse osmosis unit is used to remove trace amounts of lead. In some cases, a bisulfide iron removal system is also part of the water purification system with the iron oxidized and then removed by an ion exchange column. These systems all fail when they are called on to handle more than trace amounts of lead or other dissolved metals since the removal media rapidly becomes clogged or loaded.
In plating operations extremely high lead contents in strong acid are encountered. This type of lead removal can be handled with a electrolytic process plating part of the lead from a solution that is then reused to provide lead free acid and wash baths without creating waste. The use of hazardous chromates or sulfides can also be allowed in these chemist controlled systems. The plating cleanup systems are typically multi step processes with many chemical checks between stages.
At present, there is no simple and effective method to remove lead from washwater streams. As a result major costs are encountered in every lead project that follows the rules in waste washwater disposal.